The detected composite video signal in television receivers includes pulses which occur during the retrace intervals of the video signal. These blanking pulses are transmitted at "black level" so that the electron gun or guns of the cathode ray tube are turned off during the time that the deflection voltages are causing the electron beams to retrace. Blanking pulses are included for both the horizontal and vertical retrace intervals.
Although the horizontal and vertical blanking pulses are included in the received composite video signal, it has long been the practice to utilize auxiliary blanking pulses to assure complete blanking of the cathode ray tube during retrace. Such auxiliary blanking pulses are typically derived from the horizontal and vertical deflection circuitry and applied to the video amplifier.
The video processing system can also include automatic control circuitry such as that disclosed in Rhee et al. U.S. Pat. No. 3,947,631 or the cross-reference to co-pending application. Video processing by such systems typically requires additional blanking to prevent the automatic control circuitry from "setting-up" on retrace interval signals included in the composite video signal. Since the video processing circuitry is typically fabricated in integrated circuit form, it is desirable to include the blanking circuitry in the same integrated circuit.
The retrace pulses which are applied to the blanking circuit in typical television receivers can be derived from various points in the deflection circuits. Such retrace pulses can be either positive-going or negative-going depending upon the point in the deflection circuit from which they are developed. It is highly desirable, however, to have a single integrated circuit design which can be used in all television receivers. Known prior art blanking circuits, however, can accommodate only positive-going or only negative-going retrace pulses or, alternatively, require different input pins for the different pulses. Since additional pins on an integrated circuit require additional expense and connections to the integrated circuit are a primary source of failure, it is highly desirable to avoid the necessity of separate inputs to the blanking circuit.